Conducting varnish



Patented June 6, 1933 UNITED STATES PATENT OFFICE HANS SCHUHMANN, OF BERLIN-CHARLOTTENBURG, GERMANY, ASSIGNOR TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK CONDUCTING VARNISH No Drawing. Application filed January 21, 1930, Serial No. 422,489, and in Germany January 25, 1929.

This invention relates to a conducting varnish.

t is the object of this invention to produce a conducting varnish for use wherever such a product is necessary or desirable.

For measuring purposes and also generally, in the construction of electrical machines and apparatus, it is often required that surfaces of like electrical potential be produced. Such surfaces may be obtained, for instance, by the use of metal foil which may be produced in a galvanic way or by means of a metal spraying process. These processes involve certain disadvantages. It is diflicult to apply metal foil free from blistering, especially in the case of bodies of complicated shape. Metal spraying equipment is not available everywhere and requires special technique. The galvanic application of metal coatings is for the most part prohibitive.

The present invention avoids the disadvantages mentioned and employs a conducting varnish for the production of such coatings. It has not been possible to obtain a conducting coating by mixing a varnish which in itself is always an insulator, with a conductor such as graphite, soot, metallic dust, et cetera. Coatings thus produced show either no conductivity at all or only chance conductivity at a few points. This is probably the case because the insulating varnish surrounds the particles of conducting material so that when the varnish is applied the coating produced is an insulator. It is possible by increasing the amount of conducting material employed with the varnish to obtain a coating which is a better electrical conductor but the amount of conducting material which must be used with the varnish is such that a wholly unsuitable product for use results.

In accordance with the present invention, it has been found that the addition of certain quantities of non-conducting filling media re-' sults in varnishes which insure a perfect, even through-passage of the current. According to one method of carrying out the invention, any suitable varnish is mixed with a suitable quanity of a non-conducting filling medium and a suitable quantity of a conducting material such as graphite, soot, metallic dust, and the like. For example, a suitable conducting varnish may be obtained by mixing about 50% of an oil varnish with about 40% of lithopone and about 10% of soot and diluting to the desired consistency. A varnish of this description when applied to a carrier such as paper, fabric, and the like, after drying, shows a perfectly even conductivity in all directions. In place of the lithopone any non-conducting filling material, which is preferably non-hygroscopic and insoluble in water, may be used, such for example as magnesium carbonate, calcium carbonate, pumice, diatomaceous earth.

Such a conducting varnish may find varied use. For example, in the radio industry it may be employed to advantage in the manufacture of grid-leak resistors and in shielding.

What I claim as new and desire to secure by Letters Patent of the United States, is,--

1. A conducting varnish consisting of a mixture consisting principally of an oil varnish and lithopone and a relatively minor proportion of carbon.

2. A conducting varnish consisting of a mixture of about 50% oil varnish, about 40% of lithopone and about 10% of soot.

In witness whereof, I have hereunto set my hand this 3rd day of January, 1930.

HANS SCHUHMANN. 

